Argo44, that was a dumb asssss, lucky shot, not any expression of my skill. I had nightmares longer than you could imagine. Worse my wife had warned me I was going out into bear country and better be careful. I wasn’t and my wife gave me hell about it. My shot was desperation, a Hail Mary. It was perfect, in-spite of my lack of preparation.
When I was planning a Africa trip, which never happened, I shot a ton of .375 and .458 trying to get ready for any emergency. A charging bear is the North American version of charging big cat or buff. No bullet is too big, if well placed and none are big enough if poorly placed. But you got to shoot to have any chance and a 9mm should give you a lot of chances on a short time. Get him the gun, get him to practice a bit and make sure he keeps it on his person. Just like a rifle in the truck was not where it was needed, a pistol in a backpack will be impossible to quickly access. Get him a comfortable carry holster and have him wear it all the time. Hope he never needs it but am glad you are thinking about plan b for him.
